I absolutely recommend Diamonds-USA. I spent hours on-line researching engagement rings, diamonds, retailers, on-line retailers etc. I ended up with Diamonds-USA for a couple of reasons.
Their diamond selection was extensive. I love that they provide you with 10x magnified pictures of your actual diamond. There is no sales tax. With Blue Nile that would have added another $400 to my ring just because I happen to living in Washington state. I also loved their settings and that I could choose the metal the setting is made of.
I ordered my ring and because we were going to be out of town I asked for them to delay delivery and have it delivered on a specific day when I knew we would be at the house all day. They were happy to do it and sure enough it arrived the day I requested. I spoke with them several times over the phone and via e-mail for various reasons and each time they were extremely friendly and helpful.
My ring is gorgeous and exactly what I wanted!!!